delete IPsec phase 1 SA

Hi, I got a VPN tunneling between 2 fortigate. VPN was still working there is only 2 days and now this is down. I click on " Bring up" and nothing happen. I can read in the logs event : 4 2012-03-07 10:39:59 notice ipsec 37134 delete_phase1_sa delete IPsec phase 1 SA 5 2012-03-07 10:39:56 notice ipsec 37127 negotiate progress IPsec phase 1 6 2012-03-07 10:39:56 notice ipsec 37127 negotiate progress IPsec phase 1 7 2012-03-07 10:39:54 notice ipsec 37127 negotiate progress IPsec phase 1 What' s going wrong with my IKE key ??? everything was good I deleted the vpn config and redo but it' s same " delete_phase1_sa" thanks for your help, regards